共查询到18条相似文献，搜索用时 250 毫秒
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为揭示地震波在地壳小尺度非均匀介质中的散射过程,更准确地描述地震波的包络展宽现象,本文基于多次各向异性散射理论,采用离散波数法求解能量密度积分方程,选取高斯型自相关函数表征的散射模式,得到S波能量密度包络。基于此,本文首先分析了单次散射和多次散射在形成S波能量密度包络中的贡献规律;然后探讨了吸收系数和总散射系数对合成S波能量密度包络的影响;最后对比了在不同散射模式下合成的S波能量密度包络的差异。结果显示:① 不同的散射模式下单次散射和多次散射对地震波散射过程的贡献规律是一致的,对于近震（震源距小于100 km）,单次散射模型可以近似合成S波能量密度包络;随着震源距增大,多次前散射模型可以更快地接近总能量密度包络;② 吸收系数增大会降低直达S波和尾波幅值,总散射系数增大会降低直达S波幅值,但使得S波尾波幅值升高;③ 前散射模式下S波能量密度包络随震源距的增大会导致峰值延迟,包络展宽,尾波衰减一致性更快等现象产生。 相似文献
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高频S波随着传播距离的增大其均方根(RMS)包络逐渐变宽,把这种现象称为S波的包络展宽现象。S波传播路径上随机分布的非均匀体对S波的多次前向散射和绕射作用是导致S波包络展宽现象的主要原因,因此可用S波的包络展宽现象来研究介质的非均匀性。采用S波包络峰值延时对S波包络展宽现象进行量化。S波包络峰值延时定义为S波初至与其RMS包络峰值最大值之间的时间差。文中对长白山天池火山区204个小震记录进行了S波包络展宽分析,研究发现长白山天池火山区小震S波包络展宽现象明显,S波包络峰值延时与震中距、频率呈正相关;运用统计学方法获取了长白山天池火山区不同频带下S波包络峰值延时与震中距之间的关系。研究结果对认识S波包络展宽的特征以及定量研究长白山天池火山区介质的非均匀性具有重要意义 相似文献
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本文采用三层地壳介质模型,讨论了地方台网记录的小近震三分向地震图S波段振幅包络形状问题.认为S波包络的规则形状主要是由于强反射界面上的一次和多次全反射波形成的.分析了地壳分层结构,震源辐射特性,介质衰减对n次全反射波振幅的影响.在此基础上,从理论上给出了从直达S波到尾波之间的S波段记录部分振幅包络形状函数和S波最大振幅.利用包络形状函数方法测定了宁夏地区介质品质因素Q值. 相似文献
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《地球物理学进展》2015,(1)
虚拟偏移距(POM)偏移方法是基于Kirchhoff积分的叠前时间偏移方法,这种方法具有改善共反射点模糊成像的优势,较少依赖速度模型,具有良好的振幅保持能力,计算成本相对较低,且在横向速度变化不太剧烈的情况下能够取得较好的成像效果,是转换波叠前时间偏移的一种重要方法.因POM方法是通过将地震波旅行时的双平方根(DSR)方程转化为以虚拟偏移距为变量的单平方根双曲线方程,这种方法的虚拟震源与虚拟检波器并非并置在一起,其传播路径符合Snell定律,可抽取真正的共转换散射点(CCSP)道集,该道集不需要倾角时差校正(DMO),形成CCSP道集的过程就等于叠前时间偏移的过程.随着AVO技术的发展,振幅的保真性在偏移过程中越来越重要.本文详细分析了初始速度、虚拟偏移距和偏移孔径对共转换散射点(CCSP)道集的影响.通过转换波POM保幅成像模型试算,结果表明,利用虚拟偏移距进行叠前时间偏移时,选择合适的虚拟偏移距间隔和偏移孔径至关重要. 相似文献
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高频S波随着传播距离的增大其均方根(RMS)包络逐渐变宽,我们把这种现象称为S波包络展宽现象.S波传播路径上随机分布的非均匀体对S波的多次前向散射和绕射作用是导致S波包络展宽现象的主要原因,因此可用S波包络展宽现象来研究介质非均匀性.本文采用S波包络峰值延时来对S波包络展宽现象进行量化.S波包络峰值延时定义为S波初至与其均方根包络峰值最大值之间的时间差.本文选用长白山天池火山区的小震记录,运用S波包络峰值延时对长白山天池火山口地区的介质非均匀性进行了评价.结果发现长白山天池火山区呈现强烈的介质非均匀性,在0~2 km深度范围内介质非均匀性表现出南部强北部弱的空间分布特征;在2~5 km深度范围内介质非均匀性的空间分布特征与频率具有相关性;天池火山区介质非均匀性具有明显的多尺度特性;强弱非均匀性接触带,往往是地震频发地带.根据地震与非均匀体在空间分布的相对位置,我们认为火山区介质非均匀性可能反映了火山早期喷发堆积物介质结构的差异. 相似文献
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本文提出一种单次散射模型，用来分析不连续无规则介质内的散射波平均密度随时间的变化。这个模型改进了原来由Ｓａｔｏ（１９７７）提出的解决球形辐射和各向同性散射问题的平均能量密度模型，其散射体波限定在特定体积中介质中。本文对不同持续时间的震源平均能量密度函数的初始部分随时间的变化作了研究。在理论上平均能量密度的优势效应，是由包含散射体的特定的体积造成的。震源脉冲持续时间对于ｔ／ｔ＿０＜１．２的地震尾波的初始部分有影响，式中ｔ是从震源发震时计起的流逝时间，ｔ＿０是体波到达后的延续时间。 相似文献
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在背景模型基础上,求解模型扰动后的地震波散射场,这是目前地震反演中的一个关键步骤.本文将计算数学中求解非线性积分方程的Adomian分解方法,应用到求解标量波散射场的Lippmann-Schwinger积分方程和Ricatti积分方程中,分别得到了散射场的Born序列解和Rytov序列解.通过一维和二维数值算例说明:在满足一定的条件下,散射场的这两种序列解稳定收敛,与传统的Born和Rytov近似解相比,引入散射序列中的高阶项可以更精确地描述地震波散射场. 相似文献
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通过对波场的时间二阶积分运算以增强地震数据中的低频成分,提出了一种可有效减小对初始速度模型依赖性的地震数据全波形反演方法—时间二阶积分波场的全波形反演方法.根据散射理论中的散射波场传播方程,推导出时间二阶积分散射波场的传播方程,再利用一阶Born近似对时间二阶积分散射波场传播方程进行线性化.在时间二阶积分散射波场传播方程的基础上,利用散射波场反演地下散射源分布,再利用波场模拟的方法构建地下入射波场,然后根据时间二阶积分散射波场线性传播方程中散射波场与入射波场、速度扰动间的线性关系,应用类似偏移成像的公式得到速度扰动的估计,以此建立时间二阶积分波场的全波形迭代反演方法.最后把时间二阶积分波场的全波形反演结果作为常规全波形反演的初始模型可有效地减小地震波场全波形反演对初始模型的依赖性.应用于Marmousi模型的全频带合成数据和缺失4Hz以下频谱成分的缺低频合成数据验证所提出的全波形反演方法的正确性和有效性,数值试验显示缺失4Hz以下频谱成分数据的反演结果与全频带数据的反演结果没有明显差异. 相似文献
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Based on the formulation of a multiple non-isotropic scattering process, a characteristic source time is introduced to define the initial impulse width of energy density at the source. An analytical expression of the initial intensity spectral density of a seismic wave is incorporated into the integral equation of seismic wave energy density. And, a recursive formula of Green’s function is derived to obtain the higher order Green’s function, which is included to describe the stronger non-isotropic scattering process. Then, the effect of the scattering pattern on the energy density envelope is investigated by the modified scattering theory. Significant differences are found in the decay of the energy density envelopes with distances using different scattering patterns. The envelope synthesized by the forward dominated scattering pattern is larger than the results obtained by the isotropic and backward dominated scattering pattern. Different scattering patterns are also used to fit the observation data from the aftershocks of the 2008 Wenchuan earthquake. It is concluded that the envelopes synthesized by the forward scattering pattern can match the data better than the isotropic and backward dominated scattering cases, and a new interpretation of the coda wave is given. Finally, using the forward dominated scattering pattern, the envelope broadening of the observed data is reproduced. 相似文献
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Modeling Full Seismogram Envelopes Using Radiative Transfer Theory with Born Scattering Coefficients
The equation of radiative transfer is used to model the transport of seismic energy in 2-D and 3-D acoustic random media.
Monte-Carlo solutions of this equation using non-isotropic Born scattering coefficients are compared to three analytical solutions:
Markov approximation, radiative transfer theory with isotropic scattering coefficients, and diffusion approximation. Additionally,
we compare to finite differences solutions of the full wave equation in 2-D. We find a good correspondence of radiative transfer
theory to Markov approximation for the case of multiple forward scattering. The comparison to radiative transfer theory with
isotropic scattering coefficients, a model frequently used in data analysis, demonstrates that in the case of forward scattering
the isotropic scattering model is not better than a diffusion approach. To compare radiative transfer theory with non-isotropic
scattering coefficients to finite differences solutions of the full wave equation, the finite source duration and the bandpass
filter process as well as the normalization of absolute amplitudes are explicitely taken into account. We find a good coincidence
of both theories for scattering parameters, which are realistic for usual Earth crust. The theory correctly describes the
unscattered direct wavefront, the envelope broadening caused by multiple forward scattering, as well as the late coda caused
by multiple wide angle scattering. For strong scattering, which can be expected for very heterogeneous media such as strato
volcanoes, the solutions of radiative transfer differ from the more complete solutions of the full wave equation. 相似文献
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Yuehua Zeng 《Pure and Applied Geophysics》2006,163(2-3):533-548
One of the many important contributions that Aki has made to seismology pertains to the origin of coda waves (Aki, 1969; Aki
and Chouet, 1975). In this paper, I revisit Aki's original idea of the role of scattered surface waves in the seismic coda.
Based on the radiative transfer theory, I developed a new set of scattered wave energy equations by including scattered surface
waves and body wave to surface wave scattering conversions. The work is an extended study of Zeng et al. (1991), Zeng (1993) and Sato (1994a) on multiple isotropic-scattering, and may shed new insight into the seismic coda wave
interpretation. The scattering equations are solved numerically by first discretizing the model at regular grids and then
solving the linear integral equations iteratively. The results show that scattered wave energy can be well approximated by
body-wave to body wave scattering at earlier arrival times and short distances. At long distances from the source, scattered
surface waves dominate scattered body waves at surface stations. Since surface waves are 2-D propagating waves, their scattered
energies should in theory follow a common decay curve. The observed common decay trends on seismic coda of local earthquake
recordings particular at long lapse times suggest that perhaps later seismic codas are dominated by scattered surface waves.
When efficient body wave to surface wave conversion mechanisms are present in the shallow crustal layers, such as soft sediment
layers, the scattered surface waves dominate the seismic coda at even early arrival times for shallow sources and at later
arrival times for deeper events. 相似文献
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Elastic wave inverse scattering theory plays an important role in parameters estimation of heterogeneous media. Combining inverse scattering theory, perturbation theory and stationary phase approximation, we derive the P-wave seismic scattering coefficient equation in terms of fluid factor, shear modulus and density of background homogeneous media and perturbation media. With this equation as forward solver, a pre-stack seismic Bayesian inversion method is proposed to estimate the fluid factor of heterogeneous media. In this method, Cauchy distribution is utilized to the ratios of fluid factors, shear moduli and densities of perturbation media and background homogeneous media, respectively. Gaussian distribution is utilized to the likelihood function. The introduction of constraints from initial smooth models enhances the stability of the estimation of model parameters. Model test and real data example demonstrate that the proposed method is able to estimate the fluid factor of heterogeneous media from pre-stack seismic data directly and reasonably. 相似文献
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基于虚拟偏移距方法的各向异性转换波保幅叠前时间偏移 总被引：2，自引：1，他引：1
In this paper, we use the method of pseudo-offset migration （POM） to complete converted wave pre-stack time migration with amplitude-preservation in an anisotropic medium. The method maps the original traces into common conversion scatter point （CCSP） gathers directly by POM, which simplifies the conventional processing procedure for converted waves. The POM gather fold and SNR are high, which is favorable for velocity analysis and especially suitable for seismic data with low SNR. We used equivalent anisotropic theory to compute anisotropic parameters. Based on the scattering wave traveltime equation in a VTI medium, the POM pseudo-offset migration in anisotropic media was deduced. By amplitude-preserving POM gather mapping, velocity analysis, stack processing, and so on, the anisotropic migration results were acquired. The forward modeling computation and actual data processing demonstrate the validity of converted wave pre-stack time migration with amplitude-preservation using the anisotropic POM method. 相似文献
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Ｔｈｅｏｒｅｔｉｃａｌｒｅｓｅａｒｃｈｅｓｏｎｔｈｒｅｅ－ｄｉｍｅｎｓｉｏｎａｌｃｏｄａｗａｖｅｓｃａｔｔｅｒｉｎｇｐｒｏｂｌｅｍＹｏｎｇ－ＡｎＮＩＥ；ＪｉａｎＺＥＮＧａｎｄＤｅ－ＹｉＦＥＮＧ（聂永安，曾健，冯德益）（ＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒ... 相似文献
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本文以IASPEI的“地震波的散射与衰减”专题报告会为主,评述了近几年在地震波散射方面的研究进展.述评所涉及的方面有:1.关于地震尾波的起源;2.大震前尾波包络的前兆性变化;3.地震尾波包络衰降的机理;4.区分散射和吸收的新方法;5.新领域的开拓和研究. 相似文献
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本文对地震逆散射的研究，旨在于为抑制层间多次波和地震波场多重散射对一次反射干扰效应提供理论依据.这对薄互层地层滤波的高频恢复、保幅弹性反演、衍射地震勘探及海洋地震勘探中的干扰消除皆具重要意义.本文基于上下行波分解及弹性波互易定理，导出横向变速介质条件下线性预测算子的表达式和反射数据的广义谱分解方程. 文中先由上覆地层广义反射透射矩阵的元素定义线性预测算子，并将其表示成一系列单程波算子的线性组合,之后将横向变速介质条件下线性预测方程表达为反射数据与线性预测算子及其逆的乘积. 对该方程的求解可获得上覆地层的线性预测算子，从而可借以求出相应的反射透射算子. 本文先将水平层状介质条件下垂直入射的一维线性预测方程推广到斜入射的情况，以此为参照，导出横向非均匀介质条件下反射数据的地震逆散射广义谱分解方程.文中也揭示了单程波地震逆散射算子、反射透射算子的性态.本文还针对水平层状介质条件，给出斜入射的数值结果. 相似文献